16066_Constructors & Destructors

7/29/2019 16066_Constructors & Destructors

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Constructors

(c++ allows objects to initializethemselves when they are

created. this automaticinitialization is performed through

the use of a constructor

function.)


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Constructor is a special memberfunction having same name as that of

its class which is used to initializesome valid values to the membervariables.


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A constructor has same name as that of theclass to which it belongs.

A constructor is executed automaticallywhenever the object is created

A constructor doesn`t have a return type, noteven void

We can declare more than one constructor in aclass. These constructor differ in thereparameter list.

If you dont provide a constructor of your ownthen the compiler generates a default

constructor(expects no parameters and hasan empty body).

A constructor can preferably be used forinitialization and not for input\output operations.


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Constructor should be declared in thepublic section of the class. If it is not

declared in public section of the classthen the whole class become private .By doing this the object of the classcreated from outside cannot invoke the

constructor which is the first memberfunction to be executed automatically.


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class CLASSNAME

{

public:CLASSNAME([parameter list]);

};


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#include

#include

class Rectangle

{private:

int length,breadth;

public:

Rectangle()

{

Length=5,breadth=6;

}


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int area()

{

int a=(length*breadth);

cout


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class integer{

int n, m;public:

integer(void);....

};

integer : : integer(void){m=0;n=0;

}


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In order to initialize various dataelements of different objects with

different values when they are created.C++ permits us to achieve this objectsby passing argument to the constructorfunction when the object are created .

The constructor that can takearguments are calledparameterizedconstructors


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class abc{int m, n;public:abc (int x, int y); // parameterizedconstructor................

.................};abc : : abc (int x, int y){m = x;

n = y;

}


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#includeclass Rectangle

{private:

int length,breadth;

public:

Rectangle(int a,int b){

length=a,breadth=b;

}


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int area()

{

int a=(length*breadth);

cout


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class rectangle {private:float height;float width;int xpos;int ypos;

public:rectangle() { xpos = 0; ypos = 0; }rectangle(float, float); // constructorvoid draw(); // draw member functionvoid posn(int, int); // position member functionvoid move(int, int); // move member function

};

rectangle::rectangle(float h, float w){height = h;width = w;

}


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A constructor which is used to initializethe value of an object by copying

values of another object of the sameclass.

Syntax

Class name(constructor name &);


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A constructor is a constructor thatcreates a new object using an existing

object of the same class and initializeseach data member of newly createdobject with corresponding data memberof existing object passed as

argumnt.since it creates a copy of anexisting object so it is called copyconstructor.


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Class counter

{

Int c;

public:

Counter(int a){

C=a;

}

Counter(counter &ob)

{cout


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Void show()

{

cout


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#includeClass code{

int id;Public:code(){}code(int a)

{id = a;}code (code & x){id = x. id;

}void display(void){cout


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#include

#include

class abc

{

int rn;float fee;

public:

abc(int a,float b)

{

rn=a;fee=b;

couty;

class abc m1(x,y);

getch();

}


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Is a member function having

same name as that of constructor

but it is preceded by a tilde(~)symbol and is executedautomatically when object of a

class is destroyed


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A destructor has same name as that of the class to which itbelongs preceded by tilde(~)sign.

A destructor is executed automatically whenever the objectis destroyed.

A destructor doesn`t have a return type, not even void andno arguments

There is only one destructor in class .

If you dont provide a destructor of your own then thecompiler generates a default destructor

A destructor can be used to deallocate memory for anobject and declared in the public section.


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A destructor function is calledautomatically when the object goes out ofscope:

(1) the function ends(2) the program ends(3) a block containing temporary variables ends(4) a delete operator is called


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Need for Destructors

To de-initialize the objects when they are

destroyed To clear memory space occupied by a

data member.


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class CLASSNAME

{

.public:

~CLASSNAME([parameter list]);

};


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#include

#includeclass counter

{

int id;public:

counter(int i)

{Id=I;

cout


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~counter()

{

cout


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Output

constructor of object with id=1

constructor of object with id=2constructor of object with id=3

End of main

destructor with id=3destructor with id=2

destructor with id=1

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16066_Constructors & Destructors